During the combustion process in an IC engine (e.g., a diesel-powered engine), sulfur is concurrently formed with carbon monoxide (CO) and hydrocarbons (HC) as various sulfur oxides (SOx). Typically, 97-99% of the total amount of SOx present in exhaust gas includes sulfur dioxide (SO2) and 1-3% includes sulfur trioxide (SO3). Thus, fuels with higher sulfur content tend to produce higher amounts of SO3. For example, fuel with sulfur content of 1000 ppm may form approximately 1-3 ppm SO3.
Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by IC engines. Conventional exhaust gas aftertreatment systems include any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust aftertreatment systems for diesel-powered IC engines include a selective catalytic reduction (SCR) catalyst to convert NOx (NO and NO2 in some fraction) into harmless nitrogen gas (N2) and water vapor (H2O) in the presence of ammonia (NH3). Generally in such conventional aftertreatment systems, an exhaust reductant, (e.g., a diesel exhaust fluid such as urea) is injected into the aftertreatment system to provide a source of ammonia, and mixed with the exhaust gas to partially reduce the SOx and/or the NOx gases. The reduction byproducts of the exhaust gas are then fluidically communicated to the catalyst included in the SCR aftertreatment system to decompose substantially all of the SOx and NOx gases into relatively harmless byproducts which are expelled out of such conventional SCR aftertreatment systems.
A major cause of breakdown and failure of conventional SCR aftertreatment systems includes contamination of the exhaust reductant with hydrocarbons. For example, the exhaust reductant can be contaminated with diesel fuel, injector cleaner (e.g., toluene), or engine oil. The hydrocarbons contaminating the exhaust reductant can super heat the selective reduction catalyst, dissolve ethylene propylene diene monomer (EPDM) seals included in an exhaust reductant tank or pump, dissolves linings from the exhaust reductant tank and lines, and can also swell a diaphragm of the exhaust reductant pump. Hydrocarbon contamination accounts for about 37% to about 50% of all failures of SCR aftertreatment systems. This results in a significant number of warranty claims from customers, as it is not always possible to determine if the failure of the SCR aftertreatment system was due to hydrocarbon contamination, which can be attributed to customer oversight.